This invention is generally directed to processes for the preparation of alloys, and more specifically, the present invention is directed to the preparation of chalcogenide alloys in high purity by simultaneously electrochemically coreducing the esters of the desired elements. In one embodiment of the present invention, for example, arsenic selenium alloys of a high purity, 99.99 percent, are obtained by simultaneously coreducing by electrochemical means the isolated substantially pure esters of selenium and arsenic. The resulting chalcogenide alloys are useful as imaging members, particularly xerographic photoconductive members in electrostatic imaging systems.
The incorporation of selenium or selenium alloys into xerographic imaging members is well known. These members can be subjected to a uniform electrostatic charge for the purpose of sensitizing the surface of the photoconductive layer, followed by exposure of an image to activating electromagnetic radiation such as light, which exposure selectively dissipates the charge in the illuminated areas of the photoconductive insulating member, and wherein a latent electrostatic image is formed in the non-illuminated areas. The resulting image may then be developed and rendered visible by depositing thereon toner particles containing resin particles and pigment particles.
Recently, there has been described layered organic and inorganic photoresponsive devices containing amorphous selenium, trigonal selenium, amorphous selenium alloys, or halogen doped selenium alloys. One such photoresponsive member is comprised of a substrate, a photogenerating layer containing metal phthalocyanine, metal free phthalocyanine, vanadyl phthalocyanine, or selenium tellurium alloys, and a transport layer containing a diamine dispersed in a resinous binder, reference U.S. Pat. No. 4,265,990.
Commercially available selenium or selenium alloys for use in electrostatic imaging systems, including the use of these materials in an imaging apparatus containing layered organic or layered inorganic photoresponsive devices are generally substantially pure, that is, for example a purity of 99.99 percent or greater is desired, since the presence of impurities has a tendency to adversely effect the imaging properties of selenium, including the electrical properties thereof, causing copy quality obtained from such devices to be relatively poor in comparison to devices wherein high purity selenium is used.
Many processes are known for the preparation of chalcogenide alloys, particularly selenium containing alloys including, for example, melt blending of the elemental substances such as selenium and arsenic in the proportions desired in the final alloy product. Thus, for example, there is disclosed in U.S. Pat. No. 3,634,134 the preparation of arsenic-selenium alloys by mixing a master alloy containing the appropriate proportions of arsenic and selenium. This method not only involves high temperatures, but in most instances, crystalline materials are not obtained. Further, in many instances, depending on the process parameters, the desired alloy does not result rather, by following the melt blending process, there is obtained a homogenous mixture of arsenic, selenium, and an arsenic selenium alloy. Additionally, in these processes, there must be selected for evaporation, high purity arsenic and high purity selenium, that is 99.99 percent pure, and processes for obtaining high purity arsenic and selenium precursors require undesirable high temperature distillations. A similar melt blending method for preparing selenium alloys is disclosed in U.S. Pat. No. 3,911,091.
Also there is disclosed in U.S. Pat. No. 4,007,255 a process for preparing stable red amorphous selenium containing thallium by precipitating selenious acid containing from about 10 parts per million to about 10,000 parts per million of thallium dioxide, with hydrazine from a solution thereof in methanol or ethanol containing not more than about 50 percent by weight of water at a temperature between about -20 degrees Centigrade and the freezing point of the solution wherein the resulting precipitate is maintained at a temperature of from about a -13 degrees Centigrade to about a -3 degrees Centigrade. Additionally U.S. Pat. No. 4,009,249 contains a similar disclosure with the exception that thallium is not contained in the material being treated.
Further disclosed in U.S. Pat. No. 3,723,105 is a process for preparing a selenium-tellurium alloy by heating a mixture of selenium and tellurium containing 1 to 25 percent by weight of tellurium to a temperature not lower than 350 degrees Centigrade causing the mixture to melt, followed by cooling gradually the molten selenium and tellurium to around the melting point of the selenium tellurium alloy at a rate not higher than 100 degrees Centigrade per hour, and subsequently quenching to room temperature within 10 minutes.
Additionally, there is disclosed in U.S. Pat. No. 4,121,981 the preparation of a selenium alloy by, for example, electrochemically codepositing selenium and tellurium onto a substrate from a solution of their ions wherein the relative amount of alloy deposited on the cathode is controlled by the concentrations of the selenium and the tellurium in the electrolyte, and by other electrochemical conditions. When the selenium tellurium layer deposited on the cathode has achieved the desired thickness, deposition is discontinued and the cathode is removed. Further, there is disclosed in U.S. Pat. No. 4,192,721 the preparation of metal chalcogenides by depositing at low current densities these materials as a smooth film on a cathod by an electroplating process. As the electrolyte there is selected for this process a metal salt dissolved in an organic polar solvent, and in which there is also dissolved the chalcogen in elemental form.
Moreover there is disclosed in U.S. Pat. No. 2,649,409, the electrodeposition of selenium on conducting surfaces. According to the disclosure of this patent selenium may be electrodeposited in its grey metallic form by utilizing an electrodeposition bath containing a supply of quadrivalent selenium cations, that is cations containing selenium in the quadrivalent state such Se.sup.+4, SeO.sup.+2. Similarly, there is disclosed in U.S. Pat. No. 2,649,410 the manufacturing of selenium rectifiers, selenium photocells, and similar devices wherein grey crystalline metallic selenium is electrodeposited on a cathode from an acidic aqueous solution of selenium dioxide. More specifically, in the process described in this patent there is added elemental particles of selenium to an aqueous acidic solution containing selenium dioxide, the particles being added in a quantity greater than the metallic selenium content of the solution, followed by accomplishing an electrodeposition of the resulting treated solution.
Recently, there has been developed simple economical chemical processes for preparing chalcogenide alloys in high purity wherein substantially pure esters of the desired elements are subjected to a reduction reaction, with for example, hydrazine or sulfur dioxide. Details of this process are described in copending application U.S. Ser. No. 405,651, filed Aug. 5, 1982, the disclosure of which is totally incoporated herein by reference.
While the process as described in the copending application is suitable for the purpose intended, there continues to be a need for other suitable processes for preparing chalcogenide alloys of high purity.
Furthermore, there continues to be a need for improved processes for preparing chalcogenide alloys of a purity of 99.99 percent, and wherein the electrical properties of the resulting product can be desirably controlled. Additionally, processes are needed for obtaining chalcogenide alloys of high purity wherein the simultaneous reduction of the corresponding pure esters is not accomplished by chemical means. Moreover, there continues to be a need for the preparation of chalcogenide alloys in high purity by electrochemical methods. Also, there continues to be a need for improved processes for preparing chalcogenide alloys by electrochemical means, wherein the process is accomplished in the presence of an organic medium, and in the absence of an aqueous medium.